1. Field of the Invention
The present invention generally relates to print head apparatus used in ink jet printers, and more particularly relates to methods and apparatus used to adhesively bond an orifice plate to the channeled body portion of an ink jet print head assembly.
2. Description of Related Art
A conventionally fabricated print head assembly for an ink jet printer typically includes a piezoelectric ceramic body portion through which a spaced apart series of parallel ink chambers extend from the front end of the body to its rear end. The open chamber ends at the rear end of the body are suitably communicated with the interior of an ink reservoir to receive ink therefrom, and an orifice plate, typically formed from a polymer material, is secured over the open front end of the body using a generally planar layer of high strength adhesive material. A spaced series of ink discharge orifice openings are formed through the orifice plate, and are aligned with and positioned over the open front ends of the body chambers.
During operation of the print head, an electrical actuation pulse is transmitted to a metallized contact area associated with a selected one of the body chambers to piezoelectrically cause the lateral constriction of its walls for the duration of the pulse. This wall constriction momentarily elevates the ink pressure within the chamber, thereby forcing a small quantity of ink, in droplet form, outwardly through its associated orifice opening for use in the overall ink jet printing process.
The rise in chamber ink pressure used to form and discharge the ink droplet correspondingly exerts a forwardly directed pressure force on the adhesively bonded orifice plate. This piezoelectrically generated pressure force has proven in many instances to be of a magnitude sufficient to cause premature failure of the print head assembly due to separation of the orifice plate from the print head body caused by tensile failure at the bond interface between the hardened adhesive material layer and the orifice plate and/or the print head body.
To a large extent this separation problem can be alleviated simply by using an adhesive material having a considerably greater bonding strength. However, adhesive material having sufficient bonding strength in this particular pressure/material application is typically very expensive and undesirably increases the overall fabrication cost of the print head assembly by a significant amount. Using conventional orifice plate/body bonding techniques, the print head designer is thus faced with a choice between two undesirable alternatives--the possibility of premature assembly failure or the reality of significantly increased assembly fabrication costs.
It can be readily seen from the foregoing that a need exists for improved methods and apparatus for adhesively bonding an orifice plate to the chambered body portion of an ink jet print head assembly. It is accordingly an object of the present invention to provide such improved methods and apparatus.